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[RFC,v1,1/2] maccess: fix writing offset in case of fault in strncpy_from_kernel_nofault()

Message ID 20221108195211.214025-2-flaniel@linux.microsoft.com
State New
Headers show
Series Fix offset when fault occurs in strncpy_from_kernel_nofault() | expand

Commit Message

Francis Laniel Nov. 8, 2022, 7:52 p.m. UTC 
From: Alban Crequy <albancrequy@microsoft.com>

If a page fault occurs while copying the first byte, this function resets one
byte before dst.
As a consequence, an address could be modified and leaded to kernel crashes if
case the modified address was accessed later.

Signed-off-by: Alban Crequy <albancrequy@microsoft.com>
Tested-by: Francis Laniel <flaniel@linux.microsoft.com>
---
 mm/maccess.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--
2.25.1
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Patch

diff --git a/mm/maccess.c b/mm/maccess.c
index 5f4d240f67ec..074f6b086671 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -97,7 +97,7 @@  long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
 	return src - unsafe_addr;
 Efault:
 	pagefault_enable();
-	dst[-1] = '\0';
+	dst[0] = '\0';
 	return -EFAULT;
 }